The present invention relates to catalysts and processes for the conversion of aromatic hydrocarbons and uses thereof in the production of aromatic hydrocarbons. In particular, the present invention relates to a novel catalyst comprising a zeolite with metal bismuth or oxides thereof supported thereon for the conversion of aromatic hydrocarbons, processes for the conversion of aromatic hydrocarbons using the catalyst, and uses thereof in the production of aromatic hydrocarbons.
A large quantity of aromatic hydrocarbons such as benzene, toluene, xylene and C9 aromatic hydrocarbons (C9 A) may be obtained from the reforming and cracking processes of the petroleum distillates. The contents of toluene and C9A generally range from 40 to 50% of the total amount of the aromatic hydrocarbons dependent on different boiling ranges of the distillate feedstock and different processing methods. Normally C9A, C10 aromatic hydrocarbons (C10 A) and aromatic hydrocarbons of more than ten carbon atoms are referred to as heavy aromatic hydrocarbons in the past. Heavy aromatic hydrocarbons are mainly derived from the side products of the cracking process of light oil for producing ethylene, the aromatic hydrocarbons extraction process in the catalytic reforming in refinery, as well as toluene disproportionation and transalkylation process. For various sources of the feedstock oil and different processing methods, an aromatic hydrocarbon combination unit of 225 thousand ton xylene output per year may produce 10 to 30 thousand tons of heavy aromatic hydrocarbons each year. C10A and aromatic hydrocarbons of more than ten carbon atoms are of little use due to their complicated compositions and high boiling points. These aromatic hydrocarbons are not suitable for use as additive components in gasoline or diesel. Only some of them may be used as solvent oil or as the feedstock for separating durene, and most of the rest are used as burning fuel, causing waste of the resources.
With the development of plastic, synthetic fiber and synthetic rubber industries in the recent years, demand for benzene and xylene increases, market prices of which are higher than that of toluene and C9A. It is an important research subject in many countries to increase the production of aromatic hydrocarbons of high value from less valuable aromatic hydrocarbons through conversion processes of aromatic hydrocarbons including hydrodealkylation, toluene disproportionation and transalkylation reactions, thus making full use of the aromatic hydrocarbon resources. Toluene disproportionation is a process in which one mole of benzene and one mole of xylene are produced from two moles of toluene. Toluene may undergo transalkylation reaction with C9A to form xylene. Toluene may undergo transalkylation reaction with C10A to form C9A. Alkyl aromatic hydrocarbons such as C9A and C10A may undergo hydrodealkylation reaction to form aromatic hydrocarbons of fewer carbon atoms. A series of catalysts and processes for such reactions have already been developed.
In the processes for toluene disproportionation and transalkylation of the aromatic hydrocarbon feedstock substantially comprising toluene and C9A, mordenite is frequently used as the catalyst. For example, U.S. Pat. Nos. 2,795,629, 3,551,510, 3,729,521; 3,780,122 and 3,849,340 disclose catalysts, feedstock compositions and reaction conditions for toluene disproportionation and transalkylation process, in which catalysts used are not mentioned to comprise bismuth. Japanese patent 49-46295 discloses a catalyst for preparing alkyl benzene, which comprises a mordenite with, supported thereon, a zirconium cocatalyst anid optionally one or more components selected from silver, bismuth, copper and lead. The catalysts in the above patents have restricted performances, thus can not resist stringent reaction conditions. Therefore, in the toluene disproportionation and transalkylation processes where the above catalysts are used, C9A and heavy aromatic hydrocarbons of more than nine carbon atoms are not convertted adequately, hence yields of desired products relatively low, energy and material consumption on industrial scale units relatively high. So they are not economical.
Catalysts for converting C10A and heavy aromatic hydrocarbons of more than ten carbon atoms have been reported. For example, Japanese patent publication 51-29131 discloses a catalyst, MoO3xe2x80x94NiO/Al2O3 (13 wt % Mo, 5 wt % Ni) composition, and a process for treating C9A and C10A feedstock with this catalyst. U.S. Pat. No. 4,172,813 discloses a catalyst composition comprising 3 wt % WO3, 5 wt % MoO3 and a support consisting of 60 wt % mordenite and 40 wt % Al2O3; over this catalyst selective hydrodealkylation and transalkylation reactions of heavy reformate are effected, among which the main reaction is the transalkylation reaction between toluene and trimethylbenzene. U.S. Pat. No. 4,341,914 discloses a process for the conversion of C10A. In these references no catalyst containing bismuth is mentioned, contents of C10A in the feedstock entering the reactor is relatively low, no more than 20%, and the main disproportionation and transalkylation reaction is between toluene and C9A.
Accordingly, one object of the present invention is to provide a novel catalyst for the conversion of aromatic hydrocarbons. The catalyst can be used in (1) disproportionation and transalkylation of aromatic hydrocarbon reactants comprising substantially toluene and C9A and/or C10A as well as in (2) hydrodealkylation and transalkylation of heavy aromatic hydrocarbons containing C9A and/or aromatic hydrocarbons of more than nine carbon atoms. The catalyst has better catalytic capacity for various kinds of conversion reactions of aromatic hydrocarbons and can be employed under stringent reaction conditions. The catalyst increases the yields of desired products such as benzene and xylene. Thus, contents of heavy aromatic hydrocarbons in the aromatic reactants to be converted can be highly increased, allowing drying and pre-purifying procedures omitted or simplified. The catalyst can improve the conversion of heavy aromatic hydrocarbons, enhance the selectivity and yields of benzene and xylene, make full use of the C9A and heavy aromatic hydrocarbon resources, lower material and energy consumption, and decrease expense.
Another object of the present invention is to provide a process for the conversion of aromatic hydrocarbons. The process overcomes the disadvantages of conventional disproportionation, transalkylation and hydrodealkylation processes that heavy aromatic hydrocarbons are restricted under a low content in the aromatic hydrocarbon reactants and that they are not suitable under stringent reaction conditions.
Still another object of the present invention is to apply said catalyst and process to the production of aromatic hydrocarbons, mainly benzene, xylene and C9A.
The catalyst for the conversion of aromatic hydrocarbons according to the present invention comprises by weight 20 to 90 parts of a crystalline aluminosilicate zeolite with a SiO2/Al2O3 molar ratio of 10 to 100, 0.05 to 10 parts of metal bismuth or oxides thereof supported on the zeolite, 0 to 5 parts of one or more types of metal(s) M or oxides thereof, M being selected from the group consisting of molybdenum, copper, zirconium, strontium, lanthanum, rhenium, iron, cobalt, nickel and silver, and 10 to 60 parts of alumina as an adhesive.
The present invention also provides a process for the conversion of aromatic hydrocarbons, in which the aromatic hydrocarbon reactants contact the catalyst of the present invention to effect the conversion reaction.
The present invention further relates to the use of the catalyst and process of the present invention for the conversion of aromatic hydrocarbons in the production of aromatic hydrocarbons such as benzene, xylene and C9A from toluene, C9A, C10A and aromatic hydrocarbons of more than ten carbon atoms.
1. Catalyst of the Present Invention for the Conversion of Aromatic Hydrocarbons and Its Preparation
The catalyst according to the present invention for the conversion of aromatic hydrocarbons comprises by weight 20 to 90 parts of a crystalline aluminosilicate zeolite with a SiO2/Al2O3 molar ratio of 10 to 100, 0.05 to 10 parts of metal bismuth or oxides thereof supported on the zeolite, 0 to 5 parts of one or more types of metal(s) M or oxides thereof, M being selected from the group consisting of molybdenum. copper, zirconium, strontium, lanthanum, rhenium, iron, cobalt, nickel and silver. and 10 to 60 parts of alumina as an adhesive.
The catalyst of the present invention may be prepared by weighing the starting materials in amounts corresponding to the predetermined composition of the final product, said starting materials including zeolite, metal bismuth or its compound, metal(s) M or oxides thereof, M being selected from the group consisting of molybdenum, copper, zirconium, strontium, lanthanum, rhenium, iron, cobalt, nickel and silver, and alumina, mixing the starting materials thoroughly, followed by extruding, drying, pelleting and calcining for activating.
The zeolite used may be natural or synthesized. Non-limiting examples of the. zeolite include mordenite, ZSM-5 zeolite and xcex2-zeolite or a mixture thereof, preferably mordenite, and more preferably hydrogen-form mordenite.
The SiO2-to-Al2O3 molar ratio of the zeolite is within the range from 10 to 100, for example 10 to 30.
In one preferred embodiment hydrogen-form mordenite with a sodium content less than 0.2 wt % is used, which mordenite may be a aluminum-lean mordenite prepared by extracting aluminum from low silica mordenite with an inorganic acid, or a hydrogen-form mordenite prepared by ion-exchanging the direct-crystallized high silica Na-mordenite with ammonium chloride or nitrate solution.
Non-limiting examples of bismuth compounds are bismuth oxide and bismuth nitrate, preferably bismuth nitrate.
Non-limiting examples of metal M compound(s) may be oxide(s) or salt(s) thereof, such as M nitrate. When M comprises molybdenum, the molybdenum compound in the starting material may take the form of ammonium molybdate.
Said mixing procedure may be carried out by kneading the starting materials or impregnating the solid materials with an aqueous solution. Said extruding, drying, pelleting and calcining procedures may be proceeded by traditional methods in the prior art.
2. Process for the Conversion of Aromatic Hydrocarbons According to the Present Invention
The present invention provides processes for the conversion of aromatic hydrocarbons, in which the aromatic hydrocarbon reactants contact the novel catalyst of the present invention to effect the conversion reactions.
The reaction conditions in said processes may be as follows:
In the presence of hydrogen, the aromatic hydrocarbon reactants flow through a gas-solid fixed bed reactor and contact the catalyst inside at a reaction temperature within the range from 300 to 600xc2x0 C., a reaction pressure within the range from 1.5 to 4.0 MPa, an aromatic hydrocarbon reactant weight hourly space velocity within the range from 0.5 to 3.0 hrxe2x88x921 and a hydrogen-to-hydrocarbon molar ratio within the range from 2 to 10.
The aromatic hydrocarbon reactants comprise one or more aromatic hydrocarbons selected from toluene, C9A, C10A and aromatic hydrocarbons of more than ten carbon atoms or mixtures thereof, may contain a certain amount of impurities, such as water, indane, trace naphthalene, methylnaphthalene, dimethylnaphthalene and non-aromatic compounds. The aromatic hydrocarbon reactants contact the novel catalyst of the present invention under the reaction conditions and there may mainly occur the following reactions:
(1) Toluene Disproportionation Reaction:
C6H5CH3+C6H5CH3xe2x86x92C6H6+C6H4(CH3)2 
(2) Hydrodealkylation Reactions of Aromatic Hydrocarbons:
C6H(CH3)5+H2xe2x86x92C6H2(CH3)4+CH4 
C6H2(CH3)4+H2xe2x86x92C6H3(CH3)3+CH4 
C6H3(CH3)3+H2xe2x86x92C6H4(CH3)2+CH4 
C6H4(CH3)2+H2xe2x86x92C6H5CH3+CH4 
C6H5CH3+H2xe2x86x92C6H6+CH4 
(3) Transalkylation Reactions of Aromatic Hydrocarbons:
C6H6+C6H3(CH3)3xe2x86x92C6H5CH3+C6H4(CH3)2 
C6H5CH3+C6H3(CH3)3xe2x86x922C6H5(CH3)2 
C6H6+C6H2(CH3)4xe2x86x92C6H5CH3+C6H3(CH3)3 
C6H5CH3+C6H2(CH3)4xe2x86x92C6H4(CH3)2+C6H3(CH3)3 
Conventional processes for toluene disproportionation and transalkylation from toluene and C9A reactants are carried out in a fixed bed reactor in the presence of hydrogen and a mordenite catalyst to produce C6xcx9cC10A, C1xcx9cC5 alkanes and a small amount of C11 aromatic hydrocarbons (C11A). Toluene and C9A in the reaction zone effluent are separated, recycled, and combined with fresh toluene and C9A outside to enter the reactor as feedstock. In toluene disproportionation and transalkylation processes or hydrodealkylation processes, heavy aromatic hydrocarbons, especially C10A and aromatic hydrocarbons of more than ten carbon atoms, may undergo accompanying side reactions such as (1) hydrocracking reactions to form saturated hydrocarbons and (2) aromatic condensation reactions to form polycyclic or fused ring compounds. The higher the reaction temperature is, the more serious the side reactions are, the more large molecule condensation products are formed, the more coke deposits on the catalyst and the quicker the activity of the catalyst decreases. C10A fraction contains trace polycyclic compounds such as naphthalene, methylnaphthalene and dimethylnaphthalene, which readily deactivate the catalyst. Therefore, as for the conversion reactions such as disproportionation and transalkylation of aromatic hydrocarbons, in order to slow the coke deposit rate on the catalyst and prolong catalyst life, it is required to run the reactions in the presence of hydrogen and to limit C10A contents in the aromatic hydrocarbon reactants to generally less than 4%, at the most no higher than 8%, and less than 2% in industrial practices. Indane is a poison to the catalyst for disproportionation and transalkylation reactions and usually controlled at less than 0.5%. The known catalysts for disproportionation and transalkylation reactions are of limited performances and can not be used for treating reactants containing high contents of C10A and aromatic hydrocarbons of more than ten carbon atoms. Since the boiling point of indane is very close to that of trimethylbenzene (TMB) in C9A, and the indane content in C9A from the top of the heavy aromatic hydrocarbon tower which provides fresh C9A for the disproportionation unit, generally must be less than 1.0% so as to meet the processing requirements, about 5xcx9c15% of C9A from the tower bottom of the heavy aromatic hydrocarbon tower is removed and can not be fully utilized.
It is surprising that the bismuth-containing zeolite catalyst of the present invention has much better catalytic properties than known catalysts. Not only does it loosen the limit for the indane content in the reaction feedstock so that the indane content may be up to 0xcx9c5 wt % of the reaction feedstock and thereby it is no longer compulsory to remove most of the indane from the starting feedstock through heavy aromatic hydrocarbon tower, thus loss of C9A during separating indane is avoided; but also does it have stronger catalytic capacity for hydrodealkylation and transalkylation reactions of C11 and C10A and can resist the poisonous impurities in heavy aromatic hydrocarbon feedstock, so that C10A can be passed into the reactor or recycled as feedstock instead of being removed from the heavy aromatic hydrocarbon tower bottom, so the utilization ratio of the heavy aromatic hydrocarbons increases, effecting good results.
Hence, in the process of the present invention for the conversion of aromatic hydrocarbons, the aromatic hydrocarbon reactants may comprise substantially a mixture of toluene and C9A in which the weight ratio of toluene to C9A is within the range from 90/10 to 10/90.
In the process of the present invention for the conversion of aromatic hydrocarbons, the aromatic hydrocarbon reactants may comprise substantially heavy aromatic hydrocarbons, such as C9A, C10A and aromatic hydrocarbons of more than ten carbon atoms or a mixture thereof.
In the process of the present invention for the conversion of aromatic hydrocarbons, the aromatic hydrocarbon reactants may comprise substantially a mixture of toluene, C10A and aromatic hydrocarbons of more than ten carbon atoms, in which the weight ratio of toluene to C10A is within the range from 90/10 to 10/90.
It is also surprising that, for the catalyst of the present invention, water content in the reactant mixture is not required to be very low. In U.S. Pat. No. 3,780,122, water content in the toluene feedstock has remarkable effect on the activity and stability of the catalyst for the toluene disproportionation reaction; even very low water content (15 ppm) can influence the toluene conversion. In this patent water content in toluene is required to be less than 25 ppm. U.S. Pat. No. 4,665,258 (1987) provides a novel improved toluene disproportionation process, in which aluminum-lean mordenite is used as a catalyst, can be carried out under stringent reaction conditions. The mordenite used in this catalyst is of a silica-to-alumina molar ratio more than 30, preferably within the range from 40 to 60. Feedstock of more than 25 ppm water content may be directly passed into the reaction zone; yet permitted water content may be within the range from 50 and 250 ppm. In the process of the present invention, the bismuth-containing zeolite catalyst used has substantially improved water resistance and can even maintain high activity and stability when the feedstock contains up to 500 ppm water. For an industrial scale unit the dehydrating procedure for the feedstock can therefore be omitted or simplified. In addition, the high activity of the present catalyst can achieve a hydrocarbon conversion ratio of, for example, up to 45% at a low reaction temperature, meanwhile preserving excellent stability, effecting very good results.
Therefore, in the process of the present invention for the conversion of aromatic hydrocarbons, water content in the aromatic hydrocarbon reactants may be up to 500 ppm.
3. Use of the Catalyst and Process of the Present Invention in the Production of Aromatic Hydrocarbons
By the process of the present invention for the conversion of aromatic hydrocarbons, benzene and toluene may be produced from feedstock substantially comprising toluene and C9A; and benzene, xylene and C9A may be produced from feedstock containing toluene, C10A and aromatic hydrocarbons of more than ten carbon atoms. A small amount of C1xcx9cC4 aliphatic hydrocarbons may be formed in each case above. Thereby, the process of the present invention may be applied to the production of benzene, xylene and C9A from feed materials of various complex compositions.
One embodiment of applying the process of the present invention to the production of benzene and xylene comprises the following steps of:
(a) separating an aromatic feedstock comprising indane, C8 aromatic hydrocarbons (C8A), C9A, C10A and C11 aromatic hydrocarbons (C11A) in a first separation zone comprising a first and a second separation tower, where a stream rich in C8A is separated from the top of the first separation tower and the bottoms product of the first tower is passed into the second separation tower, where a stream comprising indane, C9A and C10A, with an indane content of 0 to 5 wt % and a C10A content of 0 to 50 wt %, is separated from the top of the second separation tower and C11A are removed from the second tower bottom;
(b) passing the effluent stream from the top of the second separation tower along with toluene into a conversion reaction zone for the aromatic hydrocarbons, where said reaction zone is packed with the catalyst of the present invention, and the aromatic hydrocarbons are transformed, upon contacting the catalyst under conversion conditions, into a converted effluent rich in benzene and C8A; and
(c) passing said converted effluent into a second separation zone and separating them into benzene, toluene, C8A and heavy aromatic hydrocarbons containing C10A.
According to the above embodiment, toluene separated from the second separation zone can be fed into the reaction zone. A part of benzene separated from the second separation zone can be recycled into the reaction zone to increase C8A yield; however, it may be removed directly as a product instead of being recycled because recycling of benzene will lower the conversion ratio of feed toluene. The heavy aromatic hydrocarbons containing C10A separated from the second separation zone may be passed into the second separation tower of the first separation zone with or without o-xylene separated therefrom. In the feed stream entering into the conversion reaction zone, the weight ratio of toluene to C9A is within the range from 90/10 to 10/90.
By employing the novel catalyst of the present invention, limit to indane content in the aromatic feedstock is loosened, allowing it to range from 0 to 5 wt %. Therefore, it is not compulsory to separate and remove a major part of indane, which is of small amount, accompanied by the C9A feedstock through the heavy aromatic hydrocarbon tower, hence loss of C9A in indane separation process can be eliminated. Since the catalyst of the present invention enjoys strong capacity of converting C10A, C10A per se may be recycled and it is no longer necessary to remove them from the heavy aromatic hydrocarbon tower bottom, thus increasing C10A utilization ratio.